Chitosan-TiO₂-curcumin composite coatings: Toward nature-inspired, protective and sustainable silk materials

The rational use of carbohydrate polymers as functional matrices for integrating inorganic and organic components remains a key challenge in developing sustainable multifunctional materials. Here, a process-oriented, bio-inspired strategy for fabricating a chitosan-centred multifunctional composite coating is presented. This approach uniquely combines plasma-assisted activation of the silk surface, chitosan immobilisation, and subsequent controlled in situ generation of TiO₂ nanoparticles in the presence of curcumin, a naturally derived polyphenolic compound. The resulting chitosan/TiO₂/curcumin composite system simultaneously imparts antibacterial, UV-shielding, and photocatalytic self-cleaning functions to the silk. Chitosan provides strong antimicrobial activity, maintaining robust bio-barrier antibacterial protection in the composite system and achieving over 99.5% inhibition of Staphylococcus aureus and Escherichia coli growth. Curcumin acts as a TiO₂ photosensitiser and charge-transfer mediator, suppressing electron-hole recombination and enabling efficient visible-light-driven photocatalytic activity, as confirmed by accelerated Rhodamine B dye degradation and effective coffee stain removal. Complementary UV absorption by TiO₂ (UV-B) and curcumin (UV-A) delivers broad-spectrum UV protection with a UV protection factor of 32.1. Overall, this work demonstrates a distinct carbohydrate polymer-driven fabrication paradigm for engineering high-performance textiles with integrated multifunctional protective properties.